1. Field of the invention
The present invention is generally concerned with pressure vessels of the type used as pressure accumulators or transmitters, for example.
It is more particularly directed to the case where a pressure vessel of this kind comprises, within a rigid body, a diaphragm type flexible separator which, to separate two different fluids, divides the interior volume of the body into two separate chambers, an edge of the flexible separator being engaged with a support member fastened to said body which holds said edge against said inside surface of said body.
In the case of a pressure accumulator to be branch-connected to a hydraulic circuit, for example, one of the two chambers is a gas chamber, meaning a sealed chamber holding a specific quantity of gas under pressure, while the other is a liquid chamber, this other chamber being adapted to be put in communication with the hydraulic circuit concerned.
2. Description of the Prior Art
One problem to be overcome in producing pressure vessels of this type arises from the fact that the flexible separator must have a number of characteristics which are difficult to reconcile.
It must have some capacity for elastic deformation, with the result that it must be made from a deformable material, it must be temperature-resistant, and it must be capable of resisting attack by the fluids with which it comes into contact, especially the liquid in the liquid chamber, particularly when this is brake fluid, as may be the case in "ABS" type brake circuits; at the same time, it must oppose any significant diffusion of the gas in the associated gas chamber into this liquid.
Any such diffusion of gas into the liquid could interfere dangerously with the hydraulic circuit concerned.
Deformable materials with satisfactory properties in terms of their being impermeable to gases are usually incompatible with particular fluids, including brake fluid, and/or are not suitable for particular conditions of use, including those involving temperature.
To make a butyl type elastomer more gas-tight, for example, it is necessary to incorporate a filler which makes it sensitive to brake fluid.
It has long been proposed to make the flexible separator a composite member in order to dissociate the functions that it has to fulfil in order to circumvent problems of this kind.
This is the case, for example, in French patent No 1.272.420 in which the flexible separator comprises two separate walls, the outer wall of elastic material being designed to make the combination compatible with the liquid concerned while the inner wall is made from a non-elastic material chosen to be impermeable to gases.
This is also the case in French patent No 2.443.622.
In a known arrangement of the same kind the separator is made from three adjoining layers of deformable material, namely inner and outer elastic layers and an intermediate layer with low permeability to gases; it has the disadvantage that some gas can nevertheless migrate into the liquid after prolonged use.
An arrangement of this kind is referred to in the published French patent application No 2.603.075.
In this application there is disclosed the use of a gas-permeable intermediate layer constituting a kind of drain which captures the gas diffusing through the inside layer which is then evacuated to the exterior of the rigid body.
Because of the systematic loss of gas that occurs a pressure vessel of this kind necessarily has only a limited service life.
It is thus insuitable for some applications, and in particular in the "ABS" type brake circuits which are of particular relevance in this application, which must have a service life equal to that of the vehicle concerned.
If a truly gas-impermeable intermediate layer is used the problems arise in connection with this intermediate layer, both with regard to its material and its geometry.
In the French patent No 1.272.420 the gas-impermeable layer which forms a separate wall is made from polyurethane and is in the form of a kind of bellows which is deployed to a greater or lesser extent according to the quantity of gas.
Apart from the fact that a wall of this kind is difficult to make, polyurethane is not entirely satisfactory when particularly high impermeability to gases is required. Also, in the context of high-speed and numerous repetitive cycles as is the case in "ABS" type brake circuits, the mechanical strength of an intermediate layer implemented in this way may prove to be inadequate.
A general object of the present invention is an arrangement providing a particularly satisfactory and sure solution to the problem of implementing a flexible separator that is compatible with an aggressive liquid but has very high impermeability to gases, much higher than in the currently known prior art.